1. Field of the Invention
The present invention relates to a refrigerating machine oil composition. More particularly, it relates to a lubricating oil composition for use in refrigerating machine, which has excellent low temperature properties including a low flock point, excellent stability and lubricity in a Flon refrigerant, and further, a favorable compatibility with the Flon refrigerant in spite of its comparatively high viscosity. In the specification, Flon means a fluorocarbon, a chloro-fluorocarbon, a fluoro-hydrocarbon or a chlorofluoro-hydrocarbon.
2. Description of the Related Arts
Generally, refrigerating machine oils are required to have properties such as;
(1) a favorable compatibility with a refrigerant, PA1 (2) a favorable stability in contact with a refrigerant, PA1 (3) a favorable lubricity (anti-seizure property, anti-wear property). PA1 (A) 85 to 30% by weight of alkyl benzene having a kinematic viscosity at 40.degree. C. of 30 cSt or more; PA1 (B) 5 to 70% by weight of a paraffin-based mineral oil having a kinematic viscosity at 40.degree. C. of 20 to 500 cSt, a pour point of -35.degree. C. or lower, a viscosity index of 60 or more, and a sulfur content of 100 ppm or less; and PA1 (C) 1 to 30% by weight of a naphthene-based mineral oil having a kinematic viscosity at 40.degree. C. of 5 to 500 cSt, a pour point of -30.degree. C. or lower, and a sulfur content of 0.05 to 1% by weight, the total sulfur content of said composition being 0.01 to 0.10% by weight.
As refrigerating machine oils satisfying these requirements, there are known those that are improved in stability, lubricity and low temperature property by mixing different base oils and adjusting thier sulfur content (Japanese patent application Laid-Open No. 295995/1987). However, such refrigerating machine oils having a comparatively high viscosity, as used in refrigerating machine employing a rotary compressor, have problems particularly in that (i) the compatibility with Flon refrigerant is low, (ii) the two-layer separation temperature rises, (iii) a poor oil returning from evaporator occurs in the system, and (iv) the flock point rises to cause a poor low temperature property.